Caption: Giardia lamblia. Light micrograph of Giardia lamblia protozoa which parasitize the human intestine to cause giardiasis or lambliasis. Infection occurs after the ingestion of cysts in water or in contaminated food. The cysts mature to the pear-shaped adult form (seen here) in the small intestine. They attach themselves with sucking disks to the microvilli on the intestinal wall. Further cysts are produced which pass out of the host in the feces. The symptoms of infect- ion include abdominal cramps, swelling, diarrhoea and nausea; about 50% of victims show no symptoms. The disease is treated with quinacrine or metronidazole. Magnification: x400 at 35mm size.